Abstract: Room air is pulled from an inlet into a pre-filter duct and moved therethrough and through a main filter duct to an outlet in the room or some other location. The flow path is through a pre-filter unit, blower, germicidal light unit, and HEPA or ULPA filter unit to the outlet. Each of the units is readily replaceable and is furnished with a bio bag. The ducts have access openings in the duct wall at the unit locations. The access openings have flanged collars, with removable covers thereon. For installation of a unit, the bio bag is opened and secured to the flange, followed by removal of the flange cover. Then the unit is installed in the duct, the cover re-installed on the flange, and the bag rolled up in place, still attached to the flange, and remains so during operation of the apparatus and during removal of the unit at the end of its useful life, and then is used to encapsulate the used unit for disposal of the unit, to protect the service personnel from exposure to contaminants.